Although terrestrial wind engines have been built over the last few centuries, building wind turbines at sea is much more recent.
A modern wind turbine, whether for use on land or off shore, generally comprises a horizontal axis engine having a plurality of blades and an electricity generator coupled to the engine, both of them being fastened to the top end of a vertically elongate support such as a mast or pylon.
In order to reduce the cost of wind-generated energy and increase the efficiency of generators, ever more powerful generators are being fabricated that are installed in grouped manner so as to form a wind-turbine farm or field.
Increasing the power of a wind-turbine generator involves also increasing its weight and the height of the structure that supports it.
For economic reasons, it is necessary to implement wind turbines that are ever more powerful and thus of ever greater dimensions, and in particular of ever greater heights. Similarly, such wind turbines are being installed at ever greater distances from the shore and therefore in ever greater depths.
The invention applies particularly, i.e. in non-limiting manner, to wind turbines having a generator of power lying in the range 100 kilowatts (kW) to 10 megawatts (MW), the weight of such a generator possibly reaching or exceeding 300 (metric) tonnes (t) or 500 t; the length of a pylon supporting the generator may be of the order of 50 meters (m) to 100 m, and the weight of the pylon may lie in the range 100 t to 500 t.
It can thus be understood that constructing such wind turbines and installing them at sea presents great difficulties. Various solutions have been proposed for constructing and installing off-shore wind turbines.
Off-shore wind turbines are described for example in WO 01/34977 and WO 03/004870.
Wind turbines installed at sea are generally assembled on site after previously creating a foundation constituted by a pile having a diameter of several meters that is driven into the ground, its top end being provided with a flange to which an identical matching flange secured to the pylon of the wind turbine is bolted in order to ensure the assembly is fixed in the bottom in embedded manner.
Another solution consists in using a tripod resting on the ground and anchored thereto via piles driven through the base of said tripod and cemented in order to ensure that the assembly is rigid.
Another solution consists in placing a gravity-base type structure so that it rests on the sea bottom and provides anchoring as a result of its own weight, with a flange being secured to the top thereof for receiving the wind turbine that is fitted with an identical matching flange.
Under all circumstances, the fixing of the bottom end of the pylon to the base represents a point of weakness for the wind turbine. Furthermore, it is guaranteed that the wind turbine is vertical only when the plane of the flange secured to the base is accurately horizontal, i.e. when its axis is accurately vertical. Unfortunately, there is a problem of positioning the axis ZZ′ of the pylon vertically and of keeping it in the vertical position throughout the lifetime of the installation, as a result of differential compaction of the ground or of the stone covering made on the sea bottom and on which the pylon foundation or base is placed or anchored. The pylon needs to be accurately vertical so that the wind turbine operates properly throughout its lifetime, which may reach or exceed 20 to 25 years.
In general, verticality is adjusted via the flanges used for fastening the bottom end of the pylon to the base. Nevertheless, it is not simple to adjust verticality in this way and the adjustment must be extremely rigid; furthermore, it is not possible to adjust verticality very finely so as to ensure that the final verticality of the wind turbine is accurate.
In WO 2004/015207 and GB 2 394 498, systems are described for fixing and adjusting the verticality of a wind turbine pylon resting on a base on the sea bottom. However the means described do not enable the adjustment of the angle of inclination of the wind turbine pylon to be modified easily over time, and the means for fixing the pylon to the base are not sufficiently reliable in terms of accuracy and rigidity. Once the angle of inclination has been adjusted, the tubular cavity in which the bottom end of the pylon is embedded is subjected to final cementing, which tubular cavity is fully immersed.
Thus, the problem to be solved is that of making a wind turbine in which the rigidity of the embedded fixing of the pylon to the base is improved.
Another problem is to make a device for adjusting the verticality of a wind turbine pylon that is both extremely rigid and also capable of enabling said verticality to be adjusted very accurately, while being simple to operate and inexpensive to implement.
Another problem to be solved is to be able to readjust the verticality of a wind turbine during its operating lifetime, after differential compaction has occurred in the ground, where such compaction leads to the base taking up an angle of inclination relative to its theoretically horizontal position, and thus to the wind turbine pylon taking an angle of inclination relative to its theoretically vertical position, thereby running the risk in the long term of severe mechanical damage to the turret that supports the rotor and the generator of the wind engine.